The present invention relates generally to a light modulator (also referred to as a spatial light modulator), and a phase modulation type light modulator that modulates a phase distribution, and an apparatus using the same, such as an exposure apparatus and a projection display apparatus, such as a projector. This invention is suitable, for example, maskless exposure that utilizes the light modulator and dispenses with a photo-mask or reticle as an original.
A projection optical system has been conventionally used to expose a mask pattern onto a substrate on which a photosensitive agent is applied in manufacturing a semiconductor device and a liquid crystal panel. However, as the finer processing to the mask pattern and a larger mask size are demanded with the improved integration and increased area of the device, an increase of the mask cost becomes problematic. Accordingly, the maskless exposure that dispenses with the mask for exposure has called attentions.
One exemplary attractive maskless exposure is a method for projecting a pattern image onto a substrate using a phase-modulation type light modulator. The light modulator is a parallel-connected type device, and the number of pixels per unit time may possibly be increased enormously. The phase modulation needs a minute displacement of a mirror, and thus is suitable for high-speed operation. In particular, a grating light valve (“GLV”) type light modulator that uses a modulated pattern of a diffraction grating is suitable for a large amount of data transfers, and a maskless exposure apparatus that transfers enormous data amount. The maskless exposure apparatus that uses the light modulator instead of the mask to modulate the exposure light in accordance with a desired pattern, and condenses the pattern via a projection optical system, and forms the pattern on the substrate. GLV is disclosed, for example, in Optics Letters, Vol. 17, pp. 688-690 (1992).
Referring now to FIGS. 12A and 12B, a description will be given of an operational principle of a conventional GLV 20. Here, FIG. 12A shows a relationship between the section of the GLV 20 and phase differences given by the GLV 20 when the GLV 20 turns off. FIG. 12B shows a relationship between the section of the GLV 20 and phase differences given by the GLV 20 when the GLV 20 turns on.
Each element in the GLV 20 has a pair of catoptric bands or ribbons 21, and each pixel 23 includes three elements 22. The GLV 20 is a reflection-type phase modulator that has plural pixels 23 arranged in parallel. One of ribbons 21 in each element 22 is connected to a switch (not shown), and configured to vary its level, for example, when the voltage is applied to it.
In operation, when the switch turns off, as shown in FIG. 12A, all the ribbons 22 have the same level. When the switch turns on, as shown in FIG. 12B, the ribbons 21 fall alternately by a quarter of the irradiation wavelength, and the reflected light receives a phase difference of 180° between two adjacent ribbons 21. When the switch turns off, only the 0th order diffracted light is reflected since the reflected light is reflected while its phase is not modulated. On the other hand, when the switch turns on, the reflected light is phase-modulated and the ±1st order diffracted lights are reflected.
Referring now to FIG. 13, a description will be given of control over the diffracted light using the GLV 20. Here, FIG. 13 is a schematic view for explaining the control over the diffraction light using the GLV 20. A filter 32 that blocks the 0th order light is provided between a lens 31 and the GLV 20. When the switch turns off, no light is incident upon the lens 31. When the switch turns on, the ±1st order diffracted lights are incident upon the lens 31. A maskless exposure apparatus that controls the exposure light is configured when it installs the GLB 20 instead of the mask and the lens 31 is regarded as the projection optical system.
Other prior art include Japanese Patent Applications, Publication No. 11-237602 and 2003-59804.
In the maskless exposure apparatus equipped with the GLV 20 shown in FIG. 13, the projection optical system 31 should have a wide diameter to accept the ±1st order diffracted lights, causing a big apparatus. In addition, two lights incident upon the projection optical system 31 may interfere with each other and result in an unnecessary pattern. Accordingly, a combination of the GLV 20 and an oblique incident illumination is conceivable as shown in FIG. 14. When the switch turns off, this configuration does not supply the light to the lens 31 since only the 0th order light occurs. In addition, when the switch turns on, the ±1st order diffracted lights occur and one of them, which is the −1st order diffracted light in FIG. 14, enters the lens 31 by adjusting the irradiation angle onto the GLV.
As a result, a small size is enough for the projection optical system 31. In addition, only one light entering the projection optical system 31 realizes the high-quality exposure that resolves only a predetermined pattern. However, a problem of reduced exposure dose and thus lowered throughput occurs because one of the ±1st order diffracted lights is not used.